What is the voltage source What is the current source

Can a current source be understood as an ideal power supply (no internal resistance) and a resistor (this resistance is infinite, relative to the external load) in parallel, this is my understanding, I began to think that this is very reasonable, but when this current source is connected to a load, the current flowing through the external load is almost equal to the current on the ideal power supply, but when the external load becomes twice the original, according to Ohm's law, the branch current where the load is located should become half of the original, This contradicts the above almost constant current flow through it according to the characteristics of the current source, so there is only one explanation, which is that the voltage provided by the ideal power supply is not constant, it changes at the same time as the external load changes, so that the current can be kept almost constant.

The current source cannot be approximated as a voltage source and an infinite resistor in parallel, and it makes no sense to connect an infinite resistor in parallel, just like not connecting it.

The current source can be approximated as an ideal constant current source and an equivalent resistor in parallel, and the magnitude of the equivalent resistance is equal to the ratio of the output voltage to the constant current source current when the power supply is open, that is, RI=UO I

When the load resistance is large, the output voltage of the current source is high, and when the load resistance is small, the output voltage of the current source decreases, but the current is approximately unchanged.

Common power sources such as power transformers and batteries are generally approximate voltage sources rather than current sources.

The current source is generally approximated by the circuit composed of electronic devices, and it is rare for a single material or device to form a current source.

yueyezhe858

The friend's statement was incorrect: the current is constant, if the load resistance increases, how can the voltage not change? Ohm's law is violated. The mistake is that the internal resistance of the current source should not be included in the circuit analysis as a load resistance.

Circuits with current sources should be analyzed using Norton's theorem.

v=1v=1

A power supply can be represented by two different circuit models, one in the form of a voltage called a voltage source, and one in the form of a current called a current source.

1.Voltage source.

The power supply voltage U is constant equal to the electromotive force E, which is a certain value, and the current i is arbitrary, which is determined by the load resistance RL and the power supply voltage U itself, and such a power supply is called an ideal voltage source or a constant voltage source.

2.Current source.

The constant current i of the supply is a certain value, and the voltage u at both ends of the supply is arbitrary, which is determined by the load resistance rl and the current is itself. Such a power supply is called an ideal current source or a constant current source.

The power supply is divided into voltage and current, which is true.

However, the nature is somewhat different, specifically the general power supply has internal resistance, and in different load cases, it is either voltage change or current change, or both.

The concept of voltage source is easier to understand, that is, when the load changes within a certain range, the voltage does not change, such as the regulated power supply.

The current source is relatively small, but it is easy to understand, that is, when the load changes within a certain range, the current through the load remains unchanged, and by extension, the voltage on the load will of course change, of course, there are small changes and big changes, hehe.

I hope you are satisfied.

A current source is a device that can output a constant current, and it is specified that the current source cannot be open-circuited. As a result, its terminal voltage varies with external resistance.

A voltage source is a device that can output a constant voltage, and it is specified that the voltage source cannot be short-circuited. As a result, the current varies with the external resistance.

Current source: also known as constant current source, its characteristics are: the output current is a fixed value, and has nothing to do with the external circuit of the voltage.

There is no internal resistance, which is regarded as an ideal constant current source and an equivalent resistor in parallel, and the magnitude of the equivalent resistance is equal to the ratio of the output voltage to the constant current source current when the power supply is open, that is, RI=UO I

Voltage control voltage source: The voltage at both ends of the voltage source is related to the voltage at both ends of a branch.

Voltage control current source: The current passing through the current source is related to the voltage at both ends of a branch.

Current control voltage source: The voltage at both ends of the voltage source is related to the current passing through a branch.

Current control current source: The current passing through the current source is related to the current passing through a branch.

The current source voltage source can be distinguished in this way, the current source is connected to different circuits, within a certain range, the current is not changed by the change of resistance, but the voltage changes, and the voltage source is connected to different circuits, the current will change, and the voltage does not change.

A voltage source and a current source are two types of power supplies with different characteristics.

1. The voltage source is a constant voltage output, and its output voltage does not change with the change of load (theoretical definition). The output current, on the other hand, varies with the load. The alternating current commonly used in our homes is the voltage source.

The internal impedance of the voltage source is much smaller than the impedance of the load. So no matter how you use electricity, as long as it is within the range of his power, the voltage basically remains the same.

2. The current source is a constant current output, and its output current does not change with the change of load (also a theoretical definition). The output voltage varies with the load. This kind of power supply is often used in laboratories and electronic systems (such as communication, audio amplifiers), and the power is usually relatively small (of course, in some cases, there are also high-power).

His load, hopefully supplying him with a constant current output. His internal impedance tends to be large compared to the load.

3. As for when to use the voltage source, or current source. It depends on the needs of the system. Sometimes in a system, both voltage and current sources are present in different sub-circuits.

Inside the current source identification is a crossbar, which is marked with the direction of current output; Inside the voltage source identification is a vertical bar, marked with positive and negative poles. The circular logo is the ideal power supply, and the diamond shape is the controlled power supply. The controlled power supply is marked with an excitation source in the circuit.

The details are as follows:

1. The current source can be understood as an ideal power supply (no internal resistance) and a resistor (this resistance is infinite, relative to the external load) in parallel. The internal resistance of the current source is large relative to the load impedance, and the load impedance fluctuation does not change the current magnitude. The series resistance in the current source loop is meaningless because it does not change the current of the load and does not change the voltage on the load.

On the schematic, these resistors should be simplified. The load impedance is only meaningful if it is connected in parallel on the current source, and it is a shunt relationship with the internal resistance.

2. The voltage source, that is, the ideal voltage source, is a model abstracted from the actual power supply, which can always maintain a certain voltage at both ends regardless of the current flowing. A voltage source has two basic properties: first, its terminal voltage value u or a certain time function u(t) is independent of the current flowing.

Second, the voltage source itself is determined, while the current flowing through it is arbitrary.

Extended information: 1. Characteristics of ideal current source.

1. The output current is constant;

2. DC equivalent resistance is infinite;

3. The AC equivalent resistance is infinite.

Second, the direction of the voltage source current.

The current flows from the low potential of the voltage source to the high potential, and the external force overcomes the electric field force to move the positive charge [3] to do work; The voltage source emits power and acts as a power supply. On the contrary, it absorbs power and plays a load role. If a battery [4] is charged, it becomes a load.

Common voltage sources are dry batteries, accumulators, generators, etc.

What is voltage and current, novice is so easy to understand.

Current source. Namely.

Ideal current source.

It is a model abstracted from an actual power supply, where the end buttons always provide a certain amount of current to the outside, regardless of the voltage at both ends.

Voltage source. Namely.

Ideal voltage source.

It is a model abstracted from the actual power supply, in which a certain voltage is always maintained at both ends, regardless of the amount of current flowing.

The current source has two basic properties: first, whether it provides a fixed value i or a certain time function i(t) independent of the voltage at both ends. Second, the current source itself is current-determined, and the voltage across it is arbitrary.

The voltage source has two basic properties: first, it's.

Terminal voltage. The fixed value u or a certain time function u(t) has nothing to do with the current flowing. Second, the voltage source itself is determined, while the current flowing through it is arbitrary.

Extended Information: Current source classifications are:

1. Adjustable current source.

DC current source.

The main parameters have outputs.

current, rated output rate, etc.), the output current is adjustable and called an adjustable current source.

2. Pulse current. Source. Pulse.

Current mirrors. The circuit adopts high speed.

MOSFET. Implement the pair.

Constant current source. Replication and multiplication of current, reducing the output load of the pulse current source to the pre-amp.

Deep negative feedback.

Part of the influence, raised.

Stability of the circuit.

And take advantage of simulation.

Multiplexer.

on the current mirror. Gate.

The control of will.

Pulse signal. It is transferred to the pulse current and thus the pulse current is output.

3. High-precision current source.

A high-precision one is proposed.

Current source circuit.

By the V i transformation, it will be by.

Band gap datum. Electricity.

The bandgap reference voltage independent of temperature and power supply voltage generated by the voltage circuit is converted into a high-precision reference current independent of temperature and voltage, and the required mirror current is generated by the high-precision current mirror structure, which effectively suppresses the voltage.

temperature, supply voltage,

Load impedance. and the effect of interference on the current source.

Encyclopedia. Voltage source.

Encyclopedia - Current source.

In this experiment, according to a DC regulated power supply, it has a small internal resistance within a certain current range. Therefore, in practice, it is often regarded as an ideal voltage source, that is, its output voltage does not change with the load current. The outer characteristic curve, i.e., its volt-ampere characteristic curve u f(i), is a straight line parallel to the i axis.

In practice, a constant current source can be regarded as an ideal current source within a certain voltage range, that is, its output current does not change with the voltage at both ends of the load (i.e. the resistance value of the load). The terminal voltage (or output current) of an actual voltage source (or current source) cannot be independent of the load because it has a certain internal resistance. Therefore, in the experiment, a small resistance (or large resistance) is used to connect a voltage regulator source (or constant current source) in series (or parallel) to simulate an actual voltage source (or current source).

An actual power supply, in terms of its external characteristics, can be seen as both a voltage source and a current source. If it is regarded as a voltage source, it can be represented by a combination of an ideal voltage source us and a resistor RO in series; If it is regarded as a current source, it can be expressed by the combination of an ideal current source is and a conductance GO in parallel. If there are two power supplies that can supply the same amount of current and terminal voltage to the same size resistor, then the two power supplies are said to be equivalent, that is, they have the same external characteristics.

The conditions for the equivalent conversion of a voltage source and a current source are:

Conversion of voltage source to current source: is us ro, go 1 ro current source to voltage source: us isro, ro go understands that any actual power supply can be represented by a circuit with constant electromotive force e and internal resistance r0 in series, the voltage source is to supply power to the load in the form of output voltage, and the magnitude of the output voltage can be found by:

U=e-IR0 learned from this test that the voltage source cannot be short-circuited and the current source cannot be short-circuited. When measuring the characteristics outside the voltage source, do not forget to measure the voltage value when there is no load, and when measuring the characteristics outside the current source, do not forget to measure the current value when the short circuit is measured, and pay attention to the constant current source load voltage should not exceed 20 volts, and the load should not be opened. When changing lines, the power switch must be turned off.

Attention should be paid to the polarity and range of the DC meter.

I wrote it myself, the Department of Physics, Xingtai University.